Using streptozotocin-induced diabetic Wistar rats, studies were carried out to examine the metabolic availability of vitamin A in the plasma, liver and the retina of the eye. Control and diabetic rats were fed ad lib. on a semi-purified diet either with or without (basal) vitamin A supplementation, or pair-fed on the basal diet for 4 weeks. Despite the fact that diabetic rats consumed 48% more feed, they had lower plasma concentrations of retinol (P < 0.003). The decrease in plasma retinol concentration was a response to diabetes (or diabetes-induced trauma), since neither pair-feeding (P < 0.01) nor vitamin A supplementation altered this effect (P < 0.05). Furthermore, the hepatic concentrations of the vitamin in these animals remained elevated and this increase was greater in the supplemented diabetic group (P < 0.001). Decreases in 11-cis retinal (a component of rhodopsin) concentrations in the retina were also observed in diabetic animals. The increased hepatic and the decreased plasma and retina vitamin A levels suggest a defect in the transport of the vitamin from the liver.